In most situations, the methods of the Parent Patent work reliably, allowing one system (e.g. a server system) to determine a time of capture of SPS signals (such as, for example, Global Positioning System (GPS) signals) at another system (e.g. a mobile SPS receiver/client system).
In most situations of interest the time coordination method of this invention (termed xe2x80x9cpattern matchingxe2x80x9d) works reliably. In some unusual situations, there are extremely long latencies in transmitting the signal between the mobile (e.g. mobile unit 453 of FIG. 6 of the Parent Patent) and the server (e.g. basestation 463 of FIG. 6 of the Parent Patent). This can arise if the link utilizes packet communications which allow arbitrarily long routing delays. On rare occurrences such packets may arrive after a very long period of time. Such a long latency would require that the server compare the received pattern from the mobile with a very long record stored at the server. This may be computationally complex and may require a considerable amount of time to perform the necessary computations. In addition, long latencies may give rise to ambiguities associated with the repetitions in the data patterns. For example, a substantial portion of the U.S. GPS data signal repeats at 30 second intervals, and small portions may repeat at 6 second intervals. In such circumstances the pattern match procedure may produce ambiguous results.
The present invention provides methods and apparatuses for measuring time related to satellite data messages which are used with satellite position systems, such as GPS or Glonass. A method in one embodiment comprises the steps of: (1) receiving, at an entity, a first record of at least a portion of a satellite data message; (2) comparing the first record with a second record of the satellite data message, where the first record and the second record overlap at least partially in time and where the comparing is performed after determining an estimated time when the first record was received; and (3) determining a time from the comparing, where the time indicates when the first record (e.g., the source of the first record) was received at a remote entity. In one example of this embodiment, the remote entity is a mobile SPS receiver and the entity is a basestation which communicates with the mobile SPS receiver through a wireless (and perhaps also wired) link. A method of the present invention may be performed exclusively at the basestation. In an alternative embodiment, the comparison may be performed and then the estimated time when the first record was received is used to verify that the time determined from the comparing is correct.
An embodiment of the present invention for establishing receiver timing is for the receiver to form an estimate of a portion of the satellite data message and transmit this estimate to the basestation. At the basestation this estimate is compared to a record of the satellite data message received from another GPS receiver or source of GPS information. This record is assumed to be error free. This comparison then determines which portion of the basestation""s message most closely matches the data transmitted by the remote unit. Since the basestation has read the satellite data message without error it can associate each data bit of that message with an absolute time stamp, as seen by the transmitting satellite. Hence the comparison results in the basestation assigning an appropriate time to the estimated data transmitted by the remote. This time information may be transmitted back to the remote, if desired.
A variation on the above approach is to have the basestation send a clean record of the satellite data message to the remote plus the absolute time associated with the beginning of this message. In this case the remote entity compares this record to the estimate of this data which it forms by processing a GPS signal which it receives. This comparison will provide the offset in time between the two records and thereby establish an absolute time for the locally collected data. dr
FIG. 1A is a block diagram of major components of a combined mobile SPS and communication system which can receive SPS signals and establish communication with a basestation.
FIG. 1B shows a block diagram of a typical implementation for the RF to IF converter and frequency synthesizer of FIG. 1A.
FIG. 2 is a flowchart which illustrates one method of the present invention.
FIG. 3 is a flowchart which shows another method of the present invention.
FIG. 4A shows a method performed by a mobile SPS receiver in one particular method of the present invention;
FIG. 4B shows a corresponding method performed by a basestation.
FIG. 5A shows one embodiment of a basestation of the present invention.
FIG. 5B shows another embodiment of a basestation of the present invention.
FIG. 6 shows a system of the present invention which includes an SPS receiver, a cellular telephone site, a basestation, the Internet and a client computer system.
FIG. 7 shows a simplified view of the pattern matching typically performed in the present invention in order to determine time of receipt of a satellite data message at a mobile SPS receiver.
FIG. 8A shows a method performed by a mobile SPS receiver in another particular embodiment of the invention, and
FIG. 8B shows a corresponding method performed by a basestation.
FIG. 9 shows the simplified structure of a conventional GPS receiver.
FIGS. 10A, 10B, 10C, and 10D show examples of sampled SPS signals after various stages of signal processing according to the present invention.
FIGS. 11A, 11B, and 11C show further examples of sampled SPS signals after various stages of signal processing according to the invention.
FIG. 12A shows an example of a coarse time coordination method according to one embodiment of the present invention.
FIG. 12B shows another example of a coarse time coordination method according to another embodiment of the present invention.